Many methods have been employed to measure and record the movement of the human jaw, including: mechanical, electronic, ultrasonic, electromagnetic, and optical techniques. These systems generally have a physical structure (“frame”) mounted to each of the maxilla and mandible, with the relative motion between the frames being measured and recorded. Frame-based jaw tracking systems are cumbersome, time-consuming to setup, have limited accuracy, and their presence inherently disrupts an individual's natural jaw movement. In addition, a significant practical limitation is that data obtained from frame-based systems are difficult to register to complete three-dimensional (“3D”) models of the dentition. Such registration is required to utilize these data for applications beyond basic motion characterization.
Most recently, optoelectronic systems have been reported. Generally, a mouth-piece or plastic attachments are used to hold optical imaging elements stationary with respect to the mandible and maxilla. These “clutch”-based systems are limited in that they prevent a person from closing their mouth. Additionally, the optical imaging element locations are difficult or impossible to register to the dentition.
Photogrammetry is a method for determining the geometry of objects (e.g., 3D location) from images. Photogrammetry has been used to measure jaw movement using optoelectronic systems by determining the location of targets placed on the face as well as the upper and lower arches.
Devices to aid in tracking jaw motion have been designed, but each of the previous attempts suffers certain shortcomings. Some have described a frame-based system that employs two light detectors (cameras) placed in immovable positions. This system requires an inconvenient calibration step using precisely measured target distances. Another limitation of this system is the inability to register target positions to the dentition. (See, e.g., U.S. Pat. No. 4,836,778 to Baumrind).
Others have disclosed a frame-based system using light-emitting diodes (“LEDs”) at the vertices of a triangular fixture that is held outside the mouth by a second support element bonded to the teeth. While jaw tracking data may be taken, target location cannot be accurately or conveniently related to the dentition due to the unknown offset of the LEDs from the teeth. (See, e.g., U.S. Pat. No. 5,143,086 to Duret).
Others propose a method that includes placing ‘measurement points’ on the dentition. The method assumes that the targets are not precisely on the surface, and since no means are specified for attaching the ‘jaw movement measuring points’ to the teeth, an elaborate and generalized model is presented to calculate a transform matrix to relate target positions to the dentition. In addition, the basis for this calculation requires that a subjective correspondence be made by the user between the 3D model of the dentition and the position of the targets placed on the teeth, making this procedure difficult to execute and inaccurate. (See, e.g., U.S. Pat. No. 5,905,658 to Baba).
Others describe a photogrammetry-based system that uses plastic ‘holding elements’ attached to the teeth to position ‘reference elements’ containing targets outside the oral cavity. This method also has the limitation of being unable to register the target positions to the dentition. (See, e.g., U.S. Pat. No. 4,859,181 to Neumeyer).
Others use cuboidal targets with crosshairs that are held outside the mouth. This method does not provide details as to the target attachment means. Target location data is not amenable to registering to the 3D surface of the teeth. (See, e.g., U.S. Pat. No. 5,340,309 to Robertson).
Other photogrammetry-based jaw tracking systems have been reported in the literature:
Eriksson reports a system using extraoral 5 mm diameter retro-reflective targets that are stroboscopically illuminated. A set of three targets is mounted to the upper and lower front teeth using custom acrylic fixtures, which allow the targets to protrude through the lips and be extraoral. (Eriksson, P. et al.; “Concomitant Mandibular and Head-Neck Movements During Jaw Opening-Closing in Man;” J. Oral Rehab., 1998; (25):859-870)
Kang reports using extra-orally located retro-reflective paper targets placed on a subject's head. Mandibular markers are located on a v-shaped steel rod on the labial surface of the lower incisors. (Kang, D. et al.; “A System for the Study of Jaw Movements;” J. Craniomandib. Practice, 1993; (11)63-67.)
Otake reports a system using infra-red markers attached to custom made jigs shaped for each tooth. (Otake, Y., Suzuki, N., Hattoir, A. et al.; “Real-Time Mandibular Movement Analysis System Using Four-Dimensional Cranial Bone Model;” Systems and Computers in Japan, 2006; 37(8):1216-1226.)
Missaka reports a system that uses custom fabricated maxillary and mandibular intraoral wire frames that extend from the mouth, to then hold white plastic spheres against a black background. (Missaka, R. et al.; “Development of an Experimental Optoelectronic Device to Study the Amplitude of Mandibular Movements;” Braz. Oral Res., 2008; (22)2:151-157.)
In general, the use of light emitting diodes (LEDs) as photogrammetry targets is not ideal. LEDs are relatively large, and require electrical connections in addition to some means of physical attachment to the teeth. Also, the computed location of such targets is inconsistent since LED devices do not emit light in a uniformly spherical manner, and therefore do not have the same optical signature in all viewing directions.
Previous techniques require custom fixtures to mount targets to the upper and lower dentition to keep them stationary with respect to the skull and mandible. Such attachments are time consuming to fabricate, and result in target locations that are not at precisely known locations with respect to the tooth surface. It is therefore difficult or impossible to register the computed target positions to a 3D surface model of the dentition. This is a significant limitation, since many practical applications for jaw motion data require these data to be correlated to the full dentition
Previous targets are relatively large and their center locations are less precisely determined than for smaller targets. The required camera setups are large and typically immovable and are not amenable to practical clinical use.